1. Field of the Invention
The invention relates to a process for the separation and recovery of condensable and absorbable gas components from an inert gas to be compressed. The composition of the gas mixture varies in time and the separated gas components must be compressed using a minimum of electric energy.
The condensable and absorbable gas components are gases or vapours having a critical temperature above 30.degree. C., such as ammonia, butane, propane, hydrogen sulphide, sulphur dioxide etc., and for which suitable absorbents are available.
2. Description of the Prior Art
Processes are well known which separate such condensable and absorbable components from a gas mixture using an absorbent in a washing tower. These washing processes are not complicated. What is much more difficult is the separation of the components extracted by absorption from the absorbent. In some cases this is relatively easy by way of thermal desorption, but in the case of systems which cannot be separated easily (such as extraction of C.sub.2, C.sub.3, C.sub.4 hydrocarbons from the absorbing substance) and when the separated components must be highly pure, distillation is necessary and heat is consumed.
Furthermore, the known absorption techniques cannot be used when the gas mixtures to be separated vary heavily in composition and density, which will interfere with the consistent operation of the turbo-compressor arranged downstream.
Washing out most of the gas components to be isolated on the suction side of the compressor, while reducing the quantity of residual gas to be compressed and thus the power consumed in compression, requires large quantities of absorbents to obtain residual gas of the required purity so that heat consumption during the desorption process is increased. The consumption of thermal energy, particularly of valuable energy of high parameters, can be reduced by using very low pressures or a vacuum.
However, large compressors are then required to convey the gas released back into the existing pressure systems. Usually multi-stage or multi-case compressors, designed as turbo-compressors, are necessary. These become more complicated as the desorption pressure decreases.
A disadvantage here is the high power consumption, the diminished reliability of the plant due to the complicated compressors, and the consumption of large quantities of valuable thermal energy.
If the gas mixture to be separated, or the gas-vapour-mixture, have a sufficiently high pressure, absorption is possible with reasonable amounts of absorbent by way of expansion desorption, i.e. without thermal energy. But even then the expansion gas must be recompressed into the existing gas systems. Large, multi-stage, and mostly multi-case compressors having a considerable power consumption are required in most cases, and the reliability of the process suffers. Large quantities of absorbent also have to be pressurized from the expansion pressure to the absorption pressure of the washing process, thus increasing energy requirements. Other techniques are known in which compression refrigeration is used for the partial condensation of condensable gas components. Such processes are comparatively suitable where the component to be separated has some of the properties of a refrigerant. Here too, the drawback is in the large dimensions of the compressor due to the low pressures of the refrigerant and the necessary temperatures in the refrigerant evaporator. Other shortcomings include the additional power consumption and the lower reliability of the plant due to the use of a compressor.
Absorption refrigeration plants are also being used for gas separation. The conventional absorption refrigeration plants do not use compressors, are highly reliable, and their energy consumption is only one tenth of that of compression refrigeration plants. But instead, the cooling water consumption is very high and limits the use of such plants. For plants having a high refrigerating capacity meeting the demand for heat causes problems.